staging: rtl8188eu: replace open-coded print_hex_dump()

No need to reinvent a wheel, i.e. print_hex_dump(). Replace an open-coded
variant by generic kernel helper.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>